Aristotle predicables are not that difficult to understand. They are the five ways that we can speak about something. For example you can talk about a triangle specifically (definition or species) or generally (genus). You can talk about what makes a triangle different from other shapes (differentia). You can talk about it’s unique properties (propria) and you can talk about things that aren’t really essential triangles (accidentals)
Here are Aristotle’s “predicables” explained:
- Definition or Species: a statement of the things essence (to ti en einai or “that which makes it what it is”). Aristotle called this “horos” or “definition.” Porphyry referred to this as “eidos” or “form.” Boethius introduced into the Latin tradition as “species.” It denotes the specific essence of a thing.
- Genus: Genus is that part of the essence which is also predicable of other things different from them in kind. The key to understand “genus” is that it is “general.” For example the “genus” of a triangle would be that it is a “shape.”
- Differentia: that which distinguishes one species from another within a genus. The square species and triangle species are differentiated from one another within the shape genus by the number of their sides. Triangles have three. Squares have four.
- Propria: A “property” is an attribute which is common to all the members of a class, but is not part of its essence or definition. The fact that the interior angles of all triangles are equal to two right angles is not part of the definition, but is universally true.
- Accidentia: An accident is an attribute which may or may not belong to a subject. With a “green triangle” the color green is “accidental” – it is not something essential to “triangle-ness.”
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